Although refrigeration appliances have been in existence for decades, the problems with maintaining cool temperatures inside the appliance still exist. Difficulties with power consumption, power conservation, heat dissipation, efficiency, and cost have persisted throughout the refrigeration appliance industry.
The refrigeration appliance contains numerous sources of heat dissipation and power consumption. Some primary sources are the components of the refrigeration appliance which are powered by AC voltage, e.g., compressors, fans, defrost heaters, etc. Another source is the DC power supply for the electronic components powered by DC voltage. Some DC-powered components include digital circuitry, relays, motors, solenoids, amplifiers, etc. Although the AC-powered components typically dissipate much more heat than the DC power supply, the heat dissipation of a DC supply becomes particularly troublesome if located within or near the refrigerated space, as any heat generated must ultimately be removed by the refrigeration unit. In addition, some components currently using AC power will someday be powered by the DC supply. For example, brushless DC motors can be used to power the compressor, condenser, and evaporator of a refrigeration appliance. See, e.g., U.S. Pat. No. 5,606,232 to Harlan, et al. Hence, the heat dissipation and power consumption of the DC power supply will be even more important considerations in the future.
Most DC power supplies typically involve the use of a power transformer in order to step-down the voltage from the 110 VAC line source to a lower AC voltage, such as 24 VAC. The cost of a power transformer is not insubstantial, however, and it often consumes a considerable amount of power relative to the low power required by DC loads. Heretofore, it has been proposed to provide "transformerless" power supplies wherein the transformer is replaced with a voltage and current limiting circuit, such as a capacitor in series with a resistor. These transformerless power supplies, also known as "reactive" power supplies, have significant advantages with respect to cost, component availability, size, weight, and reliability. However, prior transformerless power supplies have not been optimized to perform efficiently in a refrigeration appliance. Also, since reactive power supplies typically consume power at all times, a substantial amount of power is wasted when the refrigeration components are periodically deactivated during the refrigeration cycle.
Another possible solution is the use of a dual-output DC power supply to supply power at two different DC voltage levels in order to serve the differing power needs of various components. See, e.g., U.S. Pat. No. 5,341,284 to Huang. Although this technique can reduce overall power consumption, prior dual-output power supplies generally do not have the ability to shut down each output stage individually, which could save an even greater amount of energy. Similarly, known dual-polarity DC power supplies have individual, dual-polarity stages for providing two DC power supply outputs of opposite polarity. See, e.g., U.S. Pat. No. 4,982,318 to Maeba et al. However, the dual-polarity power supplies suffer from the same constraints as the dual-output power supplies, namely, that the individual power supplies cannot be individually controlled in order to conserve power.
In recent years, the use of electronic controls has emerged in refrigeration systems to activate and deactivate various components. Such electronic controls allow for greater efficiency and more flexibility in controlling the components of a refrigeration appliance. The control of refrigeration appliance components is well known in the art, and typically involves tracking temperature and/or time in order to determine the need for activation or deactivation of a component. See, e.g., U.S. Pat. No. 4,993,233 to Borton, et al. One such electronic controller for a refrigeration appliance is described in U.S. Pat. No. 5,479,785 to Novak, which is incorporated herein by reference. The Novak apparatus controls a refrigerator, and, more specifically, the components of the refrigerator, by selectively activating and deactivating the components from a central power supply. The selection is based on such factors as time and temperature. Although the Novak apparatus can save power consumption by deactivation of the individual components (typically saving AC power), Novak does not address power consumption by the DC power supply.
Thus, a need exists for a controlled DC power supply for reducing heat dissipation and power consumption in a refrigeration appliance.